1. Field of the Invention
The present invention relates to an optical connector and an optical module, particularly to a technique for realizing optical coupling between an optical element mounted on a board and an optical fiber at low cost.
2. Description of the Related Art
As the bit rate increases in an information device such as a computer, in-board optical coupling for connecting LSIs such as CPUs or memories by an optical fiber or optical waveguide is considered promising. In in-board optical coupling, an LSI having an optical-signal input/output function is used. Optical signals inputted to or outputted from the LSI are transmitted through an optical fiber or optical waveguide.
When LSIs mounted on a board are optically coupled to each other by an optical fiber or optical waveguide, handling of the extra length of the optical fiber or optical waveguide may be complicated. Therefore, it is preferable that an LSI and optical fiber or optical waveguide be detachable from each other. An optical module to which an optical fiber is removably attached is described in General Assembly Lecture Collected Papers C-3-123-C-3-127 (hereafter referred to as “prior document”) of The Institute of Electronics 2003.
FIG. 1 shows a sectional view of an optical module described in the prior document As shown in FIG. 1, vertical cavity surface emitting laser (VCSEL) 182, laser diode driver (LDD) 183 for driving VCSEL 182, and AC-connecting capacitor 186 are mounted on transparent resin board 181. VCSEL 182 and LDD 183 are covered with metallic shielding frame 188. Light (optical signal) emitted from VCSEL 182 enters reflection mirror 190 that is tilted to 45° through condenser lens (lens array) 184. The light entering reflection mirror 190 is reflected by reflection mirror 190 and enters optical fiber 192. Condenser lens 184 is provided in optical I/O connector holder 185. Reflection mirror 190 and optical fiber 192 are provided in optical I/O connector 191. By changing the direction of the light that is emitted from VCSEL 182 to the direction parallel with board 181 by reflection mirror 190, it is possible to lower the height of the space above board 181. LDD 183 is electrically connected with a multilayer board (BGA board 189) through a resin board (interposer 187) having a via-plug. A solder bump is used for making electrical connection between interposer 187 and BGA board 189.
Optical I/O connector 191 having reflection mirror 190 and optical fiber 192 is removably attached to optical connector holder 185. The optical axis between optical I/O connector 191 and optical connector holder 185 is adjusted by means of a not-illustrated guide pin and a through-hole formed on condenser lens 184. In this case, because the effective optical-path length from the exit plane of VCSEL 182 up to the incident plane of optical fiber 192 is large, it is difficult to obtain sufficient coupling efficiency without using a lens. In the optical module described in the prior document, sufficient coupling efficiency is secured by using condenser lens 184. Moreover, in the optical module described in the prior document, condenser lens 184 is provided on transparent resin board 181 on which VCSEL 182 is mounted. Therefore, even if the optical axis of optical fiber 192 is displaced due to insertion or removal of optical I/O connector 191, optical coupling and connection separation are performed by using a large optical beam diameter. As a result, stable optical coupling efficiency can be obtained.
However, because a reflection mirror is indispensable for the optical module described in the prior document, fabrication costs increase. Moreover, fabrication costs increase because angle adjustment of the reflection mirror is necessary. Furthermore, it is necessary to use a lens in order to obtain stable optical coupling efficiency. However, the lens is expensive and lens mounting work is costly.
To reduce the cost of the optical module, it is important to reduce the number of parts and the assembly man-hours.